(CNN) -- A day after four of Sen. John McCain's top political strategists stepped down, the co-chairman of his Florida campaign was arrested Wednesday for allegedly offering an undercover police officer money for a sex act, Titusville police said.

Florida state Rep. Bob Allen faces charges of solicitation for prostitution after he was arrested in a Titusville city park that had been under surveillance, police said.

He allegedly offered an undercover police officer $20 for the unspecified act. His attorney, Philip Lupo of Titusville, said the charge was a second-degree misdemeanor.

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"I am filing a not guilty plea. I am vigorously going to fight this," he said. "I am not resigning my office, because the people elected me [and] want me to do a good job and I am going to do a good job for them in finishing this term. ...

"This is an ugly and unpleasant situation that has been thrust upon me and my family that is not true, it is inaccurate and it is therefore not guilty."

In March, the McCain campaign issued a news release on its Florida leadership team, saying, "Allen will serve as a House co-chair for Sen. McCain's campaign."

Allen was elected to the Florida House in 2000.

His arrest comes a day after McCain's campaign manager, Terry Nelson, and chief strategist, John Weaver, announced their departures in joint statements released by the campaign. McCain's deputy campaign manager and political director also resigned this week.

Earlier this week, U.S. Sen. David Vitter, the Southern regional chairman for Rudy Giuliani's presidential campaign, was linked to the so-called D.C. Madam's escort service.

Vitter, a Louisiana Republican, said, "This was a very serious sin in my past for which I am, of course, completely responsible. Several years ago, I asked for and received forgiveness from God and from my wife in confession and marriage counseling."

It was the second blow for Giuliani's campaign. Last month, South Carolina Treasurer Thomas Ravenel, the state chairman for Giuliani's campaign, was indicted on federal cocaine charges.E-mail to a friend